The present invention relates in general to die casting machines and, in particular, to a new and useful injection piston construction having a press die and a die rod which are slidably mounted with each other and include a damping means therebetween for damping the motion of the press die as it is forcefully pushed into a mold.
In injection molding or die casting, the liquid metal is pressed at high speed with the injection piston during a so-called shot into the casting mold, to achieve a dood filling of the mold despite the progressive cooling of the casting material. At the end of the filling, the injection piston is abruptly braked by the incompressible casting material. The abrupt braking theoretically requires enormous accelerating forces, which produce high pressure peaks in the casting mold on the one hand, and in the driving system of the piston, on the other hand. These high pressure peaks exceed the closing force acting on the mold, so that keys are formed on the castings in the mold parting areas. The purpose of the present invention is to reduce the above mentioned pressure peaks at the end of a shot during the transition from filling pressure to end pressure.